1. Technical Field
The present invention relates to the use of the one-tuner smart antenna in communications receivers and is particularly directed to reducing the degradation and capture effect that can be caused by signals outside of the selected channel bandpass on power detectors, limiters, AGCs and other functions dependent on the power of signals in the selected channel bandwidth.
2. Discussion of the Prior Art
One approach well known in the art for reducing the effects of multipath and other interference is the smart antenna (see for example, Widrow, B. & others, “Adaptive antenna Systems”, Proceedings of the IEEE, Vol. 55, No. 12, December 1967, pp. 2143-2159; Monzingo, Robert A. and Miller, Thomas W., Introduction to Adaptive Antennas, John Wiley & Sons, New York, and Rappaport, Theodore S. ed., Smart Antennas, Adaptive Arravs, Algorithms, & Wireless Position Location, IEEE, Piscataway, N.J.). One problem with current smart antennas is that they require a large number of tuner components that occupy space, consume power, generate heat cause inconsistencies from antenna channel to antenna channel and increase costs. This can be a particularly significant problem for physically small and battery powered portable receivers. In many communications systems, the signal environment of the received desired signal includes signals in adjacent frequency channels or adjacent frequency bands. To reduce the interference from adjacent channel and adjacent band signals, bandpass filters or tuning bandpass filters are used to select the frequency channel of the desired signal and reject the adjacent channel and adjacent band signals. Typically for a smart antenna with N antennas, N tuners are used, where a tuner typically includes a bandpass filter (tuning bandpass filter) and a preamplifier. If the smart antenna is implemented at IF (intermediate frequency), each tuner includes a mixer to down convert the RF (radio frequency) signals to IF. Reducing the number of tuners required by the smart antenna increases the value of the smart antenna in solving a receiver interference problem, particularly in physically small and battery powered portable receivers. Reducing the number of tuners also reduces the inconsistencies from antenna channel to antenna channel. U.S. Pat. No. 6,628,969 by Kenneth Rilling addressed these problems and is incorporated by reference.
But the one-tuner smart antennas like those in U.S. Pat. No. 6,628,969 can have a distortion and capture limitation for limiters, detectors, AGC's and other functions in the wideband signal paths that depend on the power level of the signals in the selected channel bandpass. Many smart antennas include an amplitude limiter means in the antenna branch input to the weight calculation correlators to improve performance. Since the antenna element bandpass filter is no longer used, adjacent channels/bands signals that are much stronger than the desired signal can capture the gain of limiters in the antenna input signals paths. The gain of the limiter changes with the change in power of the much stronger adjacent channel/band signal(s), giving the signals of selected channel very little control over the limiter gain. This can cause reduced performance of the smart antenna.
Similarly, power detectors for determining the selected channel input power levels of this one-tuner smart antenna elements are made inaccurate by strong adjacent channels/bands signals. Also, AGC functions at the one-tuner smart antenna front end can be made to perform poorly or be captured by strong adjacent channels/bands signals. Any function that uses the selected channel or desired signal power that is dependent on the bandpass filtering in the antenna element signal path of a standard N-tuner smart antenna is either captured, made inoperable or degraded by the strong adjacent channels/bands signals in a one-tuner smart antenna.